Optical sights are used for various purposes. One example is that an optical sight can be mounted on a weapon, in order to help a user accurately aim the weapon. The optical sight accepts image information from a distance scene, and presents this image information within a field of view that is visible to the eye of a user.
In some applications, it would be desirable to integrate into the sight a rangefinder, such as a laser rangefinder, so that the user will have a tool for making an accurate determination of the distance to an actual scene or target of interest. Although various possible approaches to laser rangefinders have previously been proposed, they have not been satisfactory in all respects. For example, one possible approach would be to use separate optical apertures for the outgoing laser pulse and the incoming reflected pulse, in order to obtain high optical efficiency. In particular, in a configuration that used a single aperture and a beam splitter for the laser energy, optical energy would be lost, due to the beam splitter. Another possible approach would be to time-division multiplex the transmission optics between the laser which generates the outgoing pulse and the detector which receives the incoming reflected pulse. This approach would require a high-speed optical switch, along with high-speed and potentially high-voltage electronics to drive the switch. However, suitable high-speed optical switching technology is not readily available. Moreover, and in any event, the switches and circuits would significantly increase the size, cost and weight of any weapon sight, and would also significantly increase power consumption, so as to seriously degrade the effective battery life of a portable sight.